Xaufaxee82 It is too early to plan your trip in September, the timetables of the Eurocity between Brig and Milano Centrale are currently not published and the tickets are not available.
If you book a Supersaver Ticket, you have the timetable on your ticket and you must take the selected trains/buses. If you have a connection time of 7 minutes in Brig, it means that you have enough time to change. If you miss the connecting train due to a delay, you can take the next available train free of charge, but you should contact a ticket office to get a new reservation.
If you have another connection in Milano Centrale, it is preferable to book the entire trip until the final destination in one transaction.